DNA – Deoxyribonucleic Acid What is DNA? DNA is now used for many applications: Crime solving Paternity testing Human identification – with exception to identical twins, each person’s DNA is unique Genetic testing Tracing genealogy Identifying pathogens New vaccines Cancer therapy

DNA – what is it? DNA is the genetic material passed from parent to offspring for all of life of Earth DNA structure Francis Watson and James Crick are credited with piecing together all the information previously gathered on the molecule of DNA. They established the structure as: A double helix Having a “backbone” made of sugar and phosphates The building blocks of DNA are nucleotides. Each nucleotide consist of: A phosphate A sugar (deoxyribose) A nitrogenous base

DNA Structure There are 4 types of nitrogenous bases in DNA Cytosine (C) Thymine (T) These two are single ringed structures called pyrimidines Adenine (A) Guanine (G) These two are double ringed structures called purines The nucleotide is named according to the nitrogenous base.

DNA Structure – Base pairing rule DNA forms a double stranded helix. Base-paring takes place between a purine and pyrimidine: A = T G = C In other words, adenine and thymine are complementary base pairs; and guanine and cytosine are complementary base pairs. Hydrogen bonds connect the bases. 2 bonds between A-T and 3 bonds between G-C

Anti - parallel DNA is made up of two strands The two strands of DNA are anti- parallel This means that each side has an opposite orientation One side will have the 3’ (3 prime) carbon of the sugar in the “upward” position, whereas the other strand will have the 5’ carbon in the upward position. In other words, one side has a free sugar (3’) and the other side has a free phosphate (5’)

DNA in the Cell DNA is a working molecule – every cell in the body contains DNA and must be ready to divide when necessary. DNA is contained in the nucleus of eukaryotes. Most prokaryotes are much simpler than eukaryotes and contain a single, circular chromosome found in an area in the cytoplasm called the nucleoid.

DNA organization in the nucleus DNA is a macromolecule (large molecule). So how does it all fit in the nucleus? DNA is twisted beyond the double helix. DNA is wrapped tightly around proteins knows as histones for form structures called nucleosomes. Nucleosomes, with their DNA wrapped tightly around them, stack onto each other to form a 30-nm-wide fiber. The fiber is coiled into a thicker more compact structure – chromatin. Chromatin compacts into chromosomes during metaphase.

DNA - Replication When a cell divides, it is important for each new cell to have a complete set of genetic information and therefore receive an identical copy of the DNA This is done using the process of DNA replication. DNA replication is also called DNA synthesis. Remember – Adenine always joins with Thymine and Guanine always joins with Cytosine. This means that the two strands are complementary to each other. AGTCATCA will have the complementary strand with the sequence TCAGTACT.

DNA – Replication: Semiconservative Parental strands of DNA separate serving as templates and produce DNA molecules that have one old and one new strand. One at a time, nucleotides line up along the template strand according to the base-pairing rules the nucleotides are linked to form new strands. The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells!

DNA – Replication: Semiconservative DNA Helicase: Unwinds and unzips the DNA strands at the replication fork. DNA Polymerase: Adds the complementary nucleotides to the original strand traveling in opposite directions. Enzymes proofread DNA and repair mistake toe the 2 strands of DNA

RNA – Ribonucleic Acid Converts DNA’s message into protein. RNA is composed of monomers called nucleotides. Each nucleotide consists of: A phosphate A sugar – Ribose Nitrogenous bases (adenine, uracil, guanine, cystosine) RNA is single stranded RNA’s sugar is ribose RNA uses base Uracil instead of Thymine

RNA RNA is a copy of DNA used for protein synthesis. There are three types of RNA: Messenger RNA (mRNA) Carries DNA’s message to the ribosome (5-10% of all RNA) Transfer RNA (tRNA) Make up part of the ribosome (85-90% of all RNA) Ribosomal RNA (rRNA) Carries amino acids (building blocks of protein) to the ribosome ( 5% of all RNA) The Central Dogma: DNA encodes RNA; RNA encodes protein.

Protein Synthesis Transcription Translation One gene on DNA translated into RNA Translation mRNA carries message to ribosome Ribosome reads mRNA and links amino acids together, as instructed

Genetic Code – From DNA to Protein The bases A, T, C, G are the letters in DNA’s alphabet DNA uses a triplet code  three bases make a “word” Each triplet “calls” a specific amino acid

Genetic Code – from DNA to Protein mRNA carries the information on 1 gene from DNA mRNA’s message is also in 3- letter “words”  codons 64 codons: 60 specify 1 of the 20 amino acids 1 start codon 3 stop codons

Transcription Steps: A specific section of DNA unwinds, exposing one gene Along 1 strand, complimentary RNA bases bond * Uracil will bond with DNA’s Adenine Adjacent nucleotides form covalent bonds & build RNA backbone  RNA Polymerase RNA is released, DNA reforms double helix

Following Transcription mRNA has a sequence of bases complimentary to “sense” strand of DNA’s gene mRNA may be modified before it leaves nucleus mRNA moves out to cytoplasm and is “read” by ribosomes in a process called Translation.

Translation – info mRNA uses to make proteins After leaving the nucleus, the mRNA enters the cytoplasm and attaches to a ribosome. The ribosome moves along the mRNA until it finds a START CODON (AUG) tRNA binds to the mRNA strand at the start codon and brings with it the appropriate amino acid. tRNA also carries the ANTICODON

Another tRNA anticodon binds to the mRNA codon and drops off the appropriate amino acid. The amino acids bond together and this is the start of your protein. The binding continues until the ribosome reaches a STOP CODON. The amino acid chain is released.

The Genetic Code